This invention relates to a mechanism for holding a master, printing plate or the like on a cylinder of a duplicating, printing or like machine.
Printing machines are available for the production of copies with images formed on one or both sides of copy sheets. Such machines include printing couples which require master cylinders, blanket cylinders and impression cylinders. The master cylinders carry printing plates or masters with the images thereon to be duplicated.
There are various types of printing plates or masters used in printing or duplicating machines. For simplicity purposes, the term "master" or "masters" will be used at times herein to include printing plates for printing machines as well as masters for duplicating machines, all of which relate to the principles of printing techniques in the graphic arts field. In addition, it is known that masters are wrapped about a cylinder and held by both lead and trail edge holding devices. For simplification, the invention will be directed to holding the lead edge of the master, since the holding device will function in a printing mode without clamping the trail edge.
More specifically, clamping or holding devices or mechanisms are used with both unpunched and pre-punched masters. Conventionally, pre-punched masters are fabricated of metal or like material. Unpunched masters vary in materials and may be fabricated of paper, plastic or like materials, or even thin metal masters capable of being clamped.
When using unpunched masters, heretofore it has been conventional to hold the lead edge of the master in a clamping device extending transversely across the periphery of the cylinder. The clamping device customarily includes a planar anvil defining a gap with a movable clamping plate which grips the lead edge of the master against the anvil and holds the master by friction under the sheer magnitude of the clamping force. Such clamping devices create problems of slippage and often are complicated and expensive because of the forces required.
In the case of pre-punched masters, pins are inserted into the holes in the master along the lead edge thereof to lock the master onto the cylinder.
It is readily apparent that when changing a machine over from the use of unpunched to prepunched masters, or vice versa, there are losses in efficiency and production due to the downtime of the machine This is particularly critical and undesirable in industries where short run duplicating is performed.
This invention is directed to providing a universal holding device for masters of the character described, in that the device or mechanism will accommodate and hold pre-punched metal masters and unpunched masters of various materials, such as paper, plastic or the like, by the same method, in the same location and with the same mechanism. There is no downtime whatsoever in using the mechanism of this invention, except for the normal changing of the masters in short run duplicating.